This D-Mod is pretty straight-forward, but here's the basic idea:
Once the intro is finished, you can read the scroll to find out why you are there and go left. You are now in a huge wasteland. Scattered there are 8 locks that you can deactivate if you kill all the goblins in that particular screen.
Ok, 8 locks are deactived, but you're still missing one. Go to the house South-West of the wasteland and enter it. Now push the bookshelf on the far right side of the room to the left and you'll reveal an entrance. Enter it, go right a few screens and deactivate the ninth lock. A passage will open, enter it. Now go look at the poster on the wall. Oh no! You gotta rescue Arithia! Now go back to Ash, talk to him and part 1 is finished.